Fuel cell stacks are typically employed in the production of electricity. These fuel cell stacks typically consist of a plurality of fuel cells connected in series through an electrical load. Each fuel cell has a cathode with a cathode catalyst and an anode with an anode catalyst, with an electrolyte disposed therebetween, a cathode chamber, and an anode chamber. Within the fuel cell, a fuel, such as hydrogen, and an oxidant, such as oxygen, react to form electricity.
In a phosphoric acid fuel cell, for example, hydrogen reacts with oxygen to form water, heat, and electricity. At temperatures between about 300.degree. F. and 500.degree. F. and pressures ranging from about 1 to 8 atmospheres, hydrogen reacts on the anode catalyst to produce protons and free electrons. The free electrons pass through an external load and the protons pass through the electrolyte to the cathode where they react on the cathode catalyst with oxygen to form water.
The anode and cathode catalysts are typically composed of platinum (Pt) supported on carbon. The anode catalyst ionizes hydrogen to form protons and free electrons, while the cathode catalyst assists in the reduction of oxygen to form water. These catalysts, especially the anode catalyst, can easily be poisoned by carbon monoxide which often contaminates the fuel stream. The carbon monoxide adsorbs on the surface of the catalyst, blocking hydrogen oxidation sites thereby inhibiting efficient oxidation of the hydrogen and causing performance loss.
Typically, a shift converter is used to reduce the carbon monoxide content of the fuel stream, and hence reduce the degree of carbon monoxide poisoning. The shift converter converts the carbon monoxide to carbon dioxide and hydrogen via a reaction with water, thereby reducing the carbon monoxide content of the fuel stream. However, although the shift converter is effective, as with any piece of equipment, there are costs associated with its use and maintenance. Elimination of the shift converter would simplify fuel processing and reduce the cost, volume, and weight of the overall fuel cell system.
What is needed in the art is a carbon monoxide tolerant catalyst that can decrease or eliminate the need for a shift converter in fuel cell systems, thereby reducing cost and simplifying the fuel processing.